SOCKET(3N-SVR4) RISC/os Reference Manual SOCKET(3N-SVR4)
NAME
socket - create an endpoint for communication
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int socket(domain, type, protocol)
int domain, type, protocol;
DESCRIPTION
socket() creates an endpoint for communication and returns a
descriptor.
The domain parameter specifies a communications domain
within which communication will take place; this selects the
protocol family which should be used. The protocol family
generally is the same as the address family for the
addresses supplied in later operations on the socket. These
families are defined in the include file
/usr/include/sys/socket.h. There must be an entry in the
netconfig(4) file for at least each protocol family and type
required. If protocol has been specified, but no exact match
for the tuplet family, type, protocol is found, then the
first entry containing the specified family and type with
zero for protocol will be used. The currently understood
formats are:
PF_UNIX UNIX system internal protocols
PF_INET ARPA Internet protocols
The socket has the indicated type, which specifies the com-
munication semantics. Currently defined types are:
SOCK_STREAM
SOCK_DGRAM
SOCK_RAW
SOCK_SEQPACKET
SOCK_RDM
A SOCK_STREAM type provides sequenced, reliable, two-way
connection-based byte streams. An out-of-band data
transmission mechanism may be supported. A SOCK_DGRAM
socket supports datagrams (connectionless, unreliable mes-
sages of a fixed (typically small) maximum length). A
SOCK_SEQPACKET socket may provide a sequenced, reliable,
two-way connection-based data transmission path for
datagrams of fixed maximum length; a consumer may be
required to read an entire packet with each read system
call. This facility is protocol specific, and presently not
implemented for any protocol family. SOCK_RAW sockets pro-
vide access to internal network interfaces. The types
Printed 11/19/92 Page 1
SOCKET(3N-SVR4) RISC/os Reference Manual SOCKET(3N-SVR4)
SOCK_RAW, which is available only to the superuser, and
SOCK_RDM, for which no implementation currently exists, are
not described here.
protocol specifies a particular protocol to be used with the
socket. Normally only a single protocol exists to support a
particular socket type within a given protocol family. How-
ever, multiple protocols may exist, in which case a particu-
lar protocol must be specified in this manner. The protocol
number to use is particular to the communication domain in
which communication is to take place. If a protocol is
specified by the caller, then it will be packaged into a
socket level option request and sent to the underlying pro-
tocol layers.
Sockets of type SOCK_STREAM are full-duplex byte streams,
similar to pipes. A stream socket must be in a connected
state before any data may be sent or received on it. A con-
nection to another socket is created with a connect(3N)
call. Once connected, data may be transferred using read(2)
and write(2) calls or some variant of the send(3N) and
recv(3N) calls. When a session has been completed, a
close(2) may be performed. Out-of-band data may also be
transmitted as described on the send(3N) manual page and
received as described on the recv(3N) manual page.
The communications protocols used to implement a SOCK_STREAM
insure that data is not lost or duplicated. If a piece of
data for which the peer protocol has buffer space cannot be
successfully transmitted within a reasonable length of time,
then the connection is considered broken and calls will
indicate an error with -1 returns and with ETIMEDOUT as the
specific code in the global variable errno. The protocols
optionally keep sockets warm by forcing transmissions
roughly every minute in the absence of other activity. An
error is then indicated if no response can be elicited on an
otherwise idle connection for a extended period (for
instance 5 minutes). A SIGPIPE signal is raised if a pro-
cess sends on a broken stream; this causes naive processes,
which do not handle the signal, to exit.
SOCK_SEQPACKET sockets employ the same system calls as
SOCK_STREAM sockets. The only difference is that read calls
will return only the amount of data requested, and any
remaining in the arriving packet will be discarded.
SOCK_DGRAM and SOCK_RAW sockets allow datagrams to be sent
to correspondents named in sendto calls. Datagrams are gen-
erally received with recvfrom, which returns the next
datagram with its return address.
Page 2 Printed 11/19/92
SOCKET(3N-SVR4) RISC/os Reference Manual SOCKET(3N-SVR4)
An fcntl(2) call can be used to specify a process group to
receive a SIGURG signal when the out-of-band data arrives.
It may also enable non-blocking I/O and asynchronous notifi-
cation of I/O events with SIGIO signals.
The operation of sockets is controlled by socket level
options. These options are defined in the file
/usr/include/sys/socket.h. setsockopt(3N) and
getsockopt(3N) are used to set and get options, respec-
tively.
RETURN VALUE
A -1 is returned if an error occurs. Otherwise the return
value is a descriptor referencing the socket.
ERRORS
The socket() call fails if:
EPROTONOSUPPORT The protocol type or the specified pro-
tocol is not supported within this
domain.
EMFILE The per-process descriptor table is
full.
EACCESS Permission to create a socket of the
specified type and/or protocol is
denied.
ENOMEM Insufficient user memory is available.
ENOSR There were insufficient STREAMS
resources available to complete the
operation.
SEE ALSO
close(2), fcntl(2), ioctl(2), read(2), write(2), accept(3N),
bind(3N), connect(3N), getsockname(3N), getsockopt(3N),
listen(3N), recv(3N), send(3N), shutdown(3N),
socketpair(3N).
Printed 11/19/92 Page 3